Method and system of surveillance processing

ABSTRACT

Surveillance of missile tracks is obtained by a satellite having a series of sensors that activate an image storage tube which is periodically slit scanned. The scan data is processed to determine when the length of the series of images is sufficient to represent a missile track and the information is transmitted to a ground control station and a ground user station. By transmitting signals the control station controls the threshold levels, blanking, and the data processing program. The user station combines the data from the satellite and the ground station to determine the location of the missile and predict its trajectory.

United States Patent Shadle [451 Oct. 17,1972

[54] METHOD AND SYSTEM OF SURVEILLANCE PROCESSING [72] Inventor: Paul W.Shadle, Miraleste, Calif.

[22] Filed: May 11, 1970 [21] Appl. No.: 48,761

[52] US. Cl ..343/112 R, 250/833 H, 343/100 ST [51] Int. Cl ..G01s 5/00[58] Field of Search....250/83.3 H, 83.3 HP; 343/77,

Grey et al. ..250/83.3 H X 3,560,971 2/1971 Alsberg et al ..343/6 XPrimary Examiner-Benjamin A. Borchelt Assistant Examiner-Richard E.Berger Attorney-Harry A. Herbert, Jr. and Julian L. Siegel 5 7 ABSTRACTSurveillance of missile tracks is obtained by a satellite having aseries of sensors that activate an image storage tube which isperiodically slit scanned. The scan data is processed to determine whenthe length of the series of images is sufficient to represent a missiletrack and the information is transmitted to a ground control station anda ground user station. By transmitting signals the control stationcontrols the threshold levels, blanking, and the data processingprogram. The user station combines the data from the satellite and theground station to determine the location of the missile and predict itstrajectory.

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JWUUUU METHOD AND SYSTEM OF SURVEILLANCE PROCESSING BACKGROUND OF THEINVENTION In the past in missile surveillance the practice has been tothreshold a sensor output so that only high intensity signals are passedon to a digital computer which then attempts to relate each signal pulseto others in its vicinity. The computer finally tests related pulseswith certain algorithms to determine the likelihood that these pointsrepresent a missile track. Such a process requires a large computer,which prohibits its use in the satellite, and the necessity ofdistributing the data to several ground stations requires multiplecomputer installations, or communications from a central station to eachground station.

In the present invention the data is processed in twodimensional form bya system that can be carried in the satellite. Missile tracks arerecognized while in twodimensional form, thus discriminating againstsingle point noise returns. Clustered returns, such as from clouds, cantriggerthe track recognition circuits also, but these can be eliminatedby automatic discrimination of area blanking from the ground uponcommand.

SUMMARY OF THE INVENTION The surveillance sensor scans at a high rate,for example in excess of elements per second, but produces few highlevel signals. A requirement peculiar to this system is the desirabilityof performing most of the data processing in orbit since the data has tobe transmitted to many user stations simultaneously.

The data produced by such a surveillance sensor consists of occasionalsingle, high intensity pulses due to noise sources internal to thecensor system such as bit errors and impulse noise, clustered highintensity pulses due to background caused by high clouds illuminated bythe sun seen under low scattering angle conditions, and high intensitysignal pulses from the rocket exhaust of the missiles. The combinationof the missile motion and repeated scanning by the sensor producestracks if the sensor output is presented on a two-dimensional display.If no track is detected after a set of scans by the slit aperture, theimage storage tube is erased.

The system of the present invention makes it possible to perform trackdetection in orbit in which command changes can be made in processingparameters to adapt to special conditions. For instance, blanking ofregions of heavy background or noisy detectors may be neces sary. It mayalso be advantageous to control the frequency of readout to adapt tospecific missile types or unusual noise conditions.

It is therefore an object of this invention to provide a method ofprocessing missile tracks by a device carried aboard a satellite.

It is still another object to provide an improved method of trackingmissiles which discriminates against single point noise returns.

These and other advantages, features and objects of the invention willbecome more apparent from the following description taken in connectionwith the illustrative embodiment in the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a pictorial diagram showing thesurveillance satellite orbiting the earth in connection with groundstations;

FIG. 2 is a block diagram showing an embodiment of the invention; and

FIG. 3 is a diagram showing the image tube in connection with themissile tracks; and

FIG. 4 is a diagram showing the relationship of the sensor array and thestorage tube.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1,there is shown satellite 11 in an orbit represented by arrow 13. Sensor15 scans area 17 of earth 19 in the direction shown by arrow 21 witharea 23 representing the instantaneous view of the sensor. Antenna 25transmits data to satellite control station 27 and user station 29. Onsatellite 11 are also located a data processor and a data transmitterand the usual support systems. Orbit 13 is so chosen that the sensor cansurvey the desired areas and data can be transmitted to ground stations27 and 29.

There are two kinds of ground stations: a satellite control station anda user station. A satellite control station keeps track of the exactsatellite position and altitude, and the sensor and processor status,and also initiates commands to the satellite to control the housekeepingfunctions. The sensor and data processing operations involve adjustmentof threshold levels, blanking of noisy areas or detectors, and changesto the data processing program. The satellite control station can alsosend basic data on satellite location and sensor calibration to the userstations via the satellite.

Within satellite 11 the output data of sensor 15 which can occupy abandwidth of up to 40 MHz is processed for missile tracks. If tracks aredetected, as will be explained later, the line-of-sight angles to thesetracks are encoded and transmitted to both control station 27 and userstation 29. User station 29 combines data from satellite 11 with thedata from satellite control station 27 to calculate predictedtrajectories of the missiles observed. In a more complete operationalsystem at least two or more satellites would be located so as to observeany particular missile launching. User station 29 would then combine thedata from all the satellites to obtain precise location of a missiletrajectory.

The central element required for the satellite detection is a twodimensional type of storage sensor, such as the ITT Storage Image TubeType FW-231, or the RCA Electrostatic Image Tube. This invention is nottailored to a specific tube, but can use any two-dimensional image tubewhich permits a long storage (up to seconds) and which allows successiveimages to be stored without destroying earlier images already instorage. The final image will then be a point-for-point sum of theimages read in.

The tube should also permit read out without destroying the image andpermit erasure upon application of a suitable signal.

The surveillance sensor 15 scans a raster containing a multiplicity of nelements in a given time and then repeats the scan. A detailedfunctional block diagram of the system is shown in FIG. 2. Sensor cancontain up to 2,000 individual detectors or elements 31. The output ofthese detectors is multiplexed by multiplexer 33 into a serial datastream and then read into image storage tube 35, as controlled bycircuits 37A in real time, one frame after another in proper spatialregistration. The data in image storage tub 35 is scanned at regularintervals, as controlled by control circuits 39, for missile tracks. Ifa missile track is found, the read out mode is switched using gate 41and the data on the location of the track is read out of the storagetube, suitably encoded using analog to digital converter 43, assembledwith sensor pointing and timing data, and sent to ground stations 27 and29 by transmitter 45.

The function of the satellite control station is to perform thehousekeeping functions for normal spacecraft functioning and sensoroperation. These functions include: measuring preset position andattitude of the satellite, predicting future position and attitude,commanding spacecraft position or attitude changes, commanding sensorpointing changes, adjusting operating parameters of sensor and sensordata processing, computing calibration constants for sensor, andtransmitting data, such as spacecraft position and attitude to thesatellite for retransmission to the underground station.

Control station 27 contains computer 47 which is programmed to do thehousekeeping work. Data is fed to computer 47 by receiver preprocessor49 which receives the transmitted information from satellite 11.Computer 47 causes command signals to be generated by command controlcircuitry 51 which is transmitted to satellite 1]. The commands arereceived by command receiver circuits 53 on satellite l1. Commands arefed to control circuits 39 and transmitter 45. The housekeeping data ofcomputer 47 is also encoded by encoder 53 and fed to data decoder 55 ofground station 29. This information can be fed directly or can betransmitted to satellite 11 and retransmitted to ground station 29.Ground station 29 receives tracking data which is fed to receiverpreprocessor 57 and then fed to computer 59 together with thehousekeeping data. Computer 59 can then determine the predictedtrajectory of the missile.

Referring to FIG. 3, when a target is observed by the surveillancesensor, a series of points 61 is generated forming a slightly curvedline on raster 63 of face 65 of the storage tube. Readout device 67 witha slit-shaped aperture is caused to scan storage tube face 65 sweepingin a direction normal to the slit as shown by arrow 69. If the apertureis parallel to the track there will be a short intense signal on theread out beam. If the aperture is normal to the track, the output signalwill be less intense but will persist for a longer time. The aperturecan then sweep back and forth, and rotate incrementally in 45 stepsafter every few sweeps, the sweep direction always remaining normal tothe aperture. If there is a track, there will be some orientation of theaperture when a long pulse will be generated indicating a track. Thiscan be caused to trigger a threshold and initiate a detailed scan andtransmission of data to the user.

The data is read into the image storage tube as it is received from theindividual detectors. The readout of the image tube can be arranged inseveral ways. For clarity, one scheme is described.

After n surveillance sensor frames have been read in, the image is readout by the slit aperture 67 during the retrace time of the surveillancesensor. If a track is detected, the read out mode is switched to adetailed scan of the neighborhood of the track by a small symmetricalaperture. The location of the track is defined by the phase of the pulsedetected by the slit aperture. Erasure can take place after thisdetailed scan or after the track is completed.

The detailed functioning of the image storage tube, the mechanism ofstorage, read in and read out, depends upon the particular tubeselected. The one-toone relationship between the image planes of thesensor and storage tube is illustrated in FIG. 4. A line of detectors 71parallel to the y direction is scanned across the image in the xdirection in the focal plane of the sensors. Read in beam in the imagestorage tube scans rapidly in the v direction in synchronism with thesampling of the individual detectors in the y direction. In addition,the beam sweeps in the :4 direction in synchronism with the scan motionof the detector array; thus each elementu v, in the image storage tubecorresponds to the scan location detector element y,. The motion of thedetector array from a starting point until it again passes the samepoint while moving in the same direction, is a frame.

In FIG. 3 the image is presented as it might appear after at least sixframes have been read in. There are a number of isolated points in thedisplay as well as one missile track. In order to detect the presence ofsuch tracks the slit-shaped aperture shown is caused to scan the image.Slit aperture 67 scans across image raster 63 successively in threeorientations as shown. For the geometry shown, the apparent length ofthe track will be least when slit 67 is in orientation No. l, and thelength will be greatest when slit 67 is in orientation No. 3. The noisepulses, if isolated, will only produce short pulses, regardless of theorientation of the slits. Thus, a long pulse resulting from the imagesappearing through slit 67 indicates the presence of a track, and thetime at which slit 67 passes over the track indicates its approximateposition. This information is then utilized to switch the read out modeto a small, symmetrical aperture which is caused to scan a small rasterin the vicinity of the track. Data continues to be read in as a track isread out, thus giving information as to the direction in which the trackadvances. The display is erased after the termination of the track, orafter a certain number of frames if no track is detected.

It is not necessary to transmit to a ground station until a track isdetected. Even when a track is detected, only a small number of elementsneed be transmitted.

In severe background or clutter clusters of background returns can berecognized by the pulse shapes obtained during the slit scan mode.Additional logic circuits can be incorporated to blank out such an area.This will reduce the coverage during a period of intense background butwould occur even if human operators are employed.

I claim:

1. A system for tracking and predicting trajectories of missilescomprising:

a. a satellite having 1. means for sensing signals emanating from misb.storing the sensed signals upon a storage raster;

siles, and 2. a rr ultlplexer fed y sa d m an c. scanning the rasterwith a slit aperture in a an Image tube y the multlplexef, directionperpendicular to the longitudinal means for Scannmg thelmage storage 5direction thereof, the scanning being repeated means detectmg the p of amlsslle from different orientations about the raster; and

track from the ip ofthe Scannmg means d. detecting the sensed signalspassing through the 6. means for encodlng the output of the detecting maperture, the time length f the detected 7 means signals and theorientation of the slit aperture ,means tragsmlttmg the output of theencod 10 being respectively indicative of a missile track and b mg g k hthe direction thereof.

T xgs g gz' g Si nals f m the Satellite 3. A method of tracking missilesaccording to claim 2 o r g g to which further comprises: 2. means forcomputing the position and trajectory a. transmitting the detected datato a ground station;

of the missiles. b an h t h d 2. A method of tracking missiles using anorbiting (fomputmgt e mlssl e trajectory a t e groun Stasatellite and aground station comprising:

a. sensing signals within viewing area of the satellite;

1. A system for tracking and predicting trajectories of missilescomprising: a. a satellite having
 1. means for sensing signals emanatingfrom missiles,
 2. a multiplexer fed by said means,
 3. an image storagetube fed by the multiplexer,
 4. means for scanning the image storagetube,
 5. means for detecting the presence of a missile track from theoutput of the scanning means,
 6. means for encoding the output of thedetecting means, and
 7. means for transmitting the output of theencoding means; and b. a ground station having
 1. means for receivingsignals from the satellite, and
 2. means for computing the position andtrajectory of the missiles.
 2. a multiplexer fed by said means,
 2. meansfor computing the position and trajectory of the missiles.
 2. A methodof tracking missiles using an orbiting satellite and a ground stationcomprising: a. sensing signals within viewing area of the satellite; b.storing the sensed signals upon a storage raster; and c. scanning theraster with a slit aperture in a direction perpendicular to thelongitudinal direction thereof, the scanning being repeated fromdifferent orientations about the raster; and d. detecting the sensedsignals passing through the slit aperture, the time length of thedetected signals and the orientation of the slit aperture beingrespectively indicative of a missile track and the direction thereof. 3.A method of tracking missiles according to claim 2 which furthercomprises: a. transmitting the detected data to a ground station; and b.computing the missile trajectory at the ground station.
 3. an imagestorage tube fed by the multiplexer,
 4. means for scanning the imagestorage tube,
 5. means for detecting the presence of a missile trackfrom the output of the scanning means,
 6. means for encoding the outputof the detecting means, and
 7. means for transmitting the output of theencoding means; and b. a ground station having